Products related to the flat display panels, such as liquid crystal display panels, organic EL devices and liquid crystal projector substrates have been used as means for transmitting information between machines and human beings in various applications. The bonded brittle material substrates used for such flat display panel-related products have a configuration in which two substrates with various electronic control circuit means and the like required for display functions formed on their inner surfaces are bonded together in such a manner that they face each other. In this configuration, a material sealed in a gap formed between the two substrates is electronically controlled by the above-described electronic control circuit, whereby the substrates serve as display devices for displaying visual images.
The methods for producing the flat display panels can be divided into methods of bonding together single-plate brittle material substrates (mother substrates) and thereafter severing the bonded substrate into flat display panels of predetermined dimensions and methods of severing mother substrates into predetermined dimensions and thereafter bonding them together. Here, methods for severing the bonded brittle material substrates are described mainly.
FIGS. 31(a) to (d) are side views schematically showing a method for severing a bonded brittle material substrate used as a flat display panel.
The figures show how a mother substrate that is a bonded brittle substrate made up of brittle material substrates and that has large dimensions, in which in the length of one side may be 1 m or more, is severed into bonded brittle material substrates of smaller dimensions. More specifically, the figures sequentially show the steps of an exemplary conventional severing procedure in which a bonded brittle material substrate is scribed at a desired severing position and then severed.
This severing method is described for a bonded glass substrate formed by bonding together a pair of glass substrates facing each other as a pair of brittle material substrates. Such a bonded brittle material substrate is used, for example, as a liquid crystal display panel. A bonded brittle material substrate 71 made up of a pair of glass substrates is severed, and one of the glass substrates is a substrate 7A and the other glass substrate is a substrate 7B.
(1) First, as shown in FIG. 31(a), a scribe line Sa is formed on the substrate 7A on the upper side of the bonded brittle material substrate 71 by scribing using a glass cutter wheel 72.
(2) Next, the bonded brittle material substrate 71 is turned over and transported to a breaking device, and as show in FIG. 31(b), the substrate 7A on the lower side is broken along the scribe line Sa by pressing a breaker bar 73 against the bonded brittle material substrate 71 on a mat 74 along the scribe line Sa.
(3) Next, without reversing the upper and lower positions of the substrate 7A and the substrate 7B, the bonded brittle material substrate 71 is transported to a scribing device, with the glass substrate 7B placed on the upper side, and as shown in FIG. 31(c), a scribe line Sb is formed on the substrate 7B by scribing using the glass cutter wheel 72.
(4) Next, the bonded brittle material substrate 71 is turned over and transported to the breaking device, and as shown in FIG. 31(d), the substrate 7B on the lower side is broken along the scribe line Sb by pressing the breaker bar 73 against the bonded brittle material substrate 71 on the mat 74 along the scribe line Sb.
By executing steps (1) to (4) described above, the bonded brittle material substrate 71 can be severed at a desired position. By performing similar scribing and breaking processes on the bonded brittle material substrate 71 in the transverse and longitudinal directions, desired bonded brittle material substrates with small dimensions can be obtained from the mother bonded brittle material substrate with large dimensions.
In such consecutive severing processes, scribing devices are used, by which a scribe line (a line of a vertical crack) is produced as described above in the thickness direction of the substrate by scribing the surface of each substrate with a cutter wheel made of carbide metal or diamond with a thickness of about 0.6 mm to about 2 mm, and severing of the substrate is carried out by further extending the vertical crack in the thickness direction of the substrate by, for example, exerting a bending moment on the scribing line. Whether few or many in number, chips (cullets) are unavoidably produced in the scribing process. The bonded brittle material substrate that has undergone the severing processes or the brittle material substrate that has been bonded after the severing are used as, for example, organic EL devices or liquid crystal display panels; however, when such cullets remain on the substrates during the severing process, abrasion can be caused to the substrates, thus becoming a cause of damage to the quality of flat display panels. For this reason, it is necessary to carry out cullet removal operations as appropriate.
However, operations to remove the cullets produced in scribing are troublesome, and moreover, it is very difficult to completely remove the cullets. When the cullets remain in the periphery of the devices used for the severing process, there is the problem that the surface of the glass substrate may be scratched by the cullets. Such scratching is not desirable for a liquid crystal display substrate, and especially for projector substrates, strict quality control is required. The reason is that even slight scratches caused on the substrate are enlarged by projection when the substrate is placed in a projector and light is applied to the substrate. Once scratches are caused on the glass substrate, its quality as a projector substrate is reduced significantly and thus reliability cannot be ensured, resulting in a reduced yield.
As bonded brittle material substrates for projectors, a combination of two glasses is used for transmissive-type projectors and a combination of a glass and a semiconductor wafer is used for reflective-type projectors. In this case, quartz glass is used as the glass because of the desired heat resistance to the radiated luminous energy. However, it is more difficult to form a crack on quartz glass by scribing than on a commonly used glass such as soda glass, and thus scribing has to be carried out with a large scribing load; accordingly, there is an important interest in providing measures preventing the occurrence of cullets, or to remove the produced cullets effectively.
The present invention was made in order to solve the above-described problems effectively, and provides a method for severing a substrate without degrading the quality that is capable of avoiding surface scratching caused by cullets produced during severing a bonded brittle material substrate and a pre-bonded single-plate brittle material substrate, in particular a projector substrate, thus improving the surface strength. Furthermore, the invention provides a method for severing a bonded brittle material substrate and a pre-bonded single-plate brittle material substrate that is capable of precisely severing the substrates along a scribe line by forming a vertical crack that reaches deep inside of the substrates, while removing cullets produced during severing of the substrates, and a severing apparatus using such method.